Author Topic: Bandit won't rev! Help me! (Read 9857 times)

Coopz · « **on:** August 17, 2006, 10:59:14 PM »

Hey everyone! As you may have read in my previous post, I recently blew up the engine in my bandit 400. I managed to find a working order second hand one on ebay, and after much hassle, managed to buy it and get it delivered from 500 miles away. Not being too mechanically gifted, I gave the engine to my mechanic to fit. He managed to put the engine in, and got it all connected up, and got it running. I was so excitd at the thought of getting back on the road, but there is a small problem. It won't rev. At all. It starts and runs fine, sounds nice, but it wont rev. It just sits at idle, even with the throttle fully open. He has tried everything (and some things twice) but can't find any problems. He has cleaned the carbs twice, checked the bits that the carbs connect to, checked the valve timing twice, checked the ignition thingumajigs, swithed the engine casing for my old one (apparantly something to do with ignition is mounted to the engine casing or something) , swapped the alternator for my old one, and probably a couple of other things I can't remember/he never mentioned.

He is struggling to think of any other possibilities, but says he is pretty sure that it's not a problem with the new engine. He thinks it is a problem somewhere else in the bike. He suggested the possibility that it might be the CDI (ECU) unit, but I'm not so sure that this would have anything to do with the revving of the bike. Fair enough if it was fuel injected, but surely not if it is carburetor run? To test the CDI he would have to send it away and get it tested, costing £35 + postage, and if they find a fault it would be £150 to fix it. I found one on ebay, but it was £250! Way above my budget. He has allready spent so many hours on it that I think I may have to sell my soul just to pay the bill at the end of all this.

So, my question to you all is, could it be the CDI unit? Or would this not affect the engine revving? What could the problem possibly be? The mechanic is all out of ideas, so I am hoping some of you knowlegable people might have a clue as to what my problem is.

Any advice, suggestions, ideas, tips, tricks, or whatever, would be greatly appreciated. I Need To Be Back On The Road!

Thanks.

Thief400 · « **Reply #1 on:** August 17, 2006, 11:47:40 PM »

Check and see if the diaphrams that lift the slides in the carbs are ripped of have holes in them

Coopz · « **Reply #2 on:** August 18, 2006, 12:45:04 AM »

Thanks, I will ask him to try that, see if that is where the problem is.

Anyone got any more suggestions? Surely some other people must have an inkling or two! Come on, any suggestions appreciated!

stormi · « **Reply #3 on:** August 18, 2006, 03:29:58 PM »

What happens if you have the tank raised, and operate the throttle manually? ( i.e. where the throttle cable attaches to the carbs? )

If you turn the idle up, does it go up, or stay the same?

Does the sound of the engine change at all if you give it full throttle? I would think if it was a spark problem, that it would bubble and gurgle as you supplied it more fuel that it's capable of burning.

How much tension is there on the throttle when you pull on it?

Sure the throttle cable is installed correctly? Routed correctly?

I figure start simple ( and inexpensive)

After that, let us know what the outcome is and hopefully we can provide a solution.

stormi · « **Reply #4 on:** August 18, 2006, 03:43:00 PM »

http://hometown.aol.co.uk/bikesparks/CDI_1.htm

http://www.bigbuckatvproducts.com/Polaris/diagnostics/cdi_testing.htm

The second link mentions that there are no tests for a CDI, that you must test everything else, then if all else is good, try the CDI.

So.... test the charging system (much harder if you can't rev the engine, but might still be possible.) For instance,... if there's not enough power going to the CDI, it won't behave...

http://www.electrosport.com/electrosport_fault_finding.html

also, there are links on this page to testing diodes and such, perhaps you can open the CDI and see? http://www.electrosport.com/05_technical_start.html

Many members here have fixed their own CDIs,... search the b4 forums for "CDI" and possibly the term "repair"

Farre · « **Reply #5 on:** August 18, 2006, 04:31:43 PM »

Well, for whatever my 2cents are worth, i'm betting my a$$ it isn't the CDI. It just doesn't make sense. I'm following Thief, should be something in the carbs..ahh, IF the throttle cable is A-OK

Coopz · « **Reply #6 on:** August 18, 2006, 04:45:30 PM »

Yeah, I read up about fixing the CDI last night, but I'm still not so sure that it would have anything to do with the CDI. The throttle cable is ok. And it sounds the exact same when you open the throttle. (I think he would have tried opening the throttle manually too, he seems to have covered everything.)

I will give him a call in a while and tell him what you all say and see if any of it makes sence to him, and hopefully there will be something in it that he still hasnt tried. From what he says the carbs are in perfect order, and no matter how he operates the throttle nothing happens. I will ask him what happens when he changes the idle, and post the results here for you to see.

Thanks for all the suggestions guys, keep 'em coming!

Farre · « **Reply #7 on:** August 18, 2006, 07:30:28 PM »

but....but....when you twist the throttle, you twist the butterfly in the carbs, changing the air flow with the according amount of fuel. It doesn't make sense it stays exactly the same!
Airbox is okay (original?)? perhaps obstructed?

How much did he look into the carbs, maybe some parts are completely faulty? now i don't know what can cause such a strange phenomenon, but it's just as if the butterflies are not moving..

Say.. what happens when you use the choke? Rev's pick up or not?

Coopz · « **Reply #8 on:** August 18, 2006, 08:38:43 PM »

I meant to ask him about the choke actually, but completely forgot. Will ask next time I speak to him. I asked him before if it could be anything to do with the airbox, but he said it wasn't that.

Someone suggested to me that it could be a blockage between the feul tank and the carbs, allowing only a certain ammount of fuel to get through, no matter how much the carbs open up because only a little fuel is getting through. I'm not very mechanically minded, as I mentioned, but it sounds to me like this might be a possible explanation. But could this be the case? surely the revs would change even a little bit, if the air intake is increased but the feuling stays the same? I'm not sure.

He has cleaned the carbs twice, and says there is no problem with them, so i think they must be in good working order. he says it also isnt the airbox, valve timing, ignition, or the throttle cable.

So far I have to ask him:
What happens when you use the choke? Do the revs change?
Can you test the charging system? What is the result?
Have you operated the throttle manually? Or just at the grip?
What happens when you turn the idle up/down?
Are the diaphrams that lift the slides in the carbs ripped or do they have holes in them?

I am working all day tomorrow (12pm till 10pm) but might get a chance to phone him on my break.

I just dont understand what the problem is. The bike would rev fine up until the point the engine blew up. I think the engine had been stressed too much and it started making a rattling noise. (this noise matched the revs, so when I revved the engine the rattle sped up to match it. Sounded a bit like a 2 stroke or a chopper or something) Apparantly, one of the valves may have gone. About 2 miles further, doing about 40mph up a hill, in about 4th gear, it started to lose power. I dropped a gear, which I never had to do for going up hills before. But it carried on losing power, and then the noise changed and sounded a whole lot worse. I thought, "uh-oh, pull over asap." But about 5 seconds later the con-rod succeeded in blasting a hole right through the front of the engine casing, and pouring engine fluid and metal shrapnel into my nice custom belly pan, as well as pouring loads of smoke out in a huge cloud behind me. Better than any stunt rider doing a burnout, I can tell you that. So, 1 second hand engine later, it will run but it wont rev. You would think the problem would be in the engine, but the mechanic says the engine is fine. He reckons the revving problem must be a seperate problem, but it must have happened at the same time as the engine exploding. Because there was no problem before.

But I'll ask him about everything you guys have mentioned so far, and any other suggestions, and hopefully I will be back on the road soon.

(I love that smiley!)

Farre · « **Reply #9 on:** August 19, 2006, 03:12:07 AM »

Well , i'm stumped

With a blockage in the fuel system it's like running on an empty tank.. So when you twist the throttle you're starving the engine and it'll bog...

Dayum

Coopz · « **Reply #10 on:** August 19, 2006, 08:42:47 PM »

Well, I e-mailed the list of suggestions and questions last night, but was working today so didnt get a chance to check me e-mails. I phoned him when I was on a break, and he said that he had found out that the CDI was definately the problem. He said he had sent me an e-mail, but tole me on the phone how he had reached his decision. It kinda made sence to me, but as long as he knows what he's talking about and how to fix it, I'm happy.

This is what he said in his e-mail:
The problem does seem to be in the cdi.
Cylinders 1&4 are the ones working with 2&3 coming in occasinally but long enough to try to rev the engine up.
Swapping the plug leads and low tension leads and therefore the coil that was 1&4 becomes 2&3 and vice versa and 1&4 still run with 2&3 cutting in again.
Therefore it is reasonable to assume that both coils are ok but the signal from the cdi is at fault.
Try to find out or email me the link to repairing the cdi or ask on the bulletin board if anybody has a spare, the part number is 32900 10d30

On the phone he told me that he had found one for £70 from a bike breakers, and he had e-mailed a contact to find out if he had one cheaper. He will find out on Monday, and will buy whichever one is cheapest. It should arrive by the end of next week, and then it's just a case of him chucking it in and hopefully that will be the end of the problem. He's 99.9% sure it will fix it, but if it doesn't, I will have a CDI unit for sale! And we will have to keep trying. But if everything goes well I will be sorted by next week.

I love this mechanic. He is always so helpful and if it is just a little thing he can fix there and then, he will do it, show you how to fix it incase it happens again, and won't charge you. Also, best of all, allthough he has spent about 20 hours in total working on the bikes engine and the reving problem, he is only going to charge me for 8 hours roughly, as he told me at the start that it would only be a 6-8 hour job. As the problem was unknown to both of us, and he couldn't find out what was wrong, he isn't going to charge me fo the extra hours spent searching for the problem. What a relief, If I had to pay for all 20 hours work, I would have to sell a couple of kidneys on ebay to get the money!

What an expensive problem.

Engine:£200
Delivery:£50
FItting and fault finding/fixing:£200
CDI Unit, plus p&p: £100

Total: £550

Just to return my bike to it's original pre-engine-blowing-up value!

Thanks to everyone for their help on this. Good to find some people who are willing to help out fellow riders! This board is excellent, wish I'd found it sooner! So full of information and friendly helpful advice.

Thanks everyone. I'll let you know how it goes once I have the new CDI unit.

interfuse · « **Reply #11 on:** August 20, 2006, 02:28:52 AM »

If the new CDI doesn't help have 'em check the wiring harness to the coil... my wiring went bad.

Farre · « **Reply #12 on:** August 20, 2006, 04:23:35 AM »

If you want a new CDI cheap, check the US Ebay, there's a guy selling it all the time. It are replica's built in Argentina, but i can safely say they're perfect! Got one in my B4 ATM for 4 months